The present invention is based on a method for deploying a restraint system.
It is known heretofore that a frontal collision of a vehicle can be detected by evaluating acceleration signals and/or summed acceleration signals that arise in the direction of driving via comparison with predefined deployment thresholds, a restraint system for protecting the people in the vehicle being deployed if the deployment thresholds are exceeded.
By contrast, the method according to the present invention for deploying a restraint system has the advantage that vehicle oscillations at right angles to the direction of driving, i.e., in the y direction, are also evaluated in order to detect a frontal collision. This oscillation is less pronounced in the case of low-speed collisions than in the case of higher-speed collisions. In the event of a collision and under certain initial conditions, the method according to the present invention uses the y signal that is determined in the restraint system""s central control system to xe2x80x9csharpenxe2x80x9d the deployment algorithm within a definable time window, so that in particular deployment performance at collision speeds of 40 to 64 km/h is improved. Herein, it is advantageous that the y acceleration signal and an integral of the y acceleration signal are evaluated, so that if necessary a value that is determined as a function of the y acceleration signal and of the integrated y acceleration signal is added to the x acceleration signal and the x integrator, respectively. Thus higher and lower deployment thresholds are reached more quickly, so that the restraint system is deployed early, which improves the safety of the occupants of the vehicle. Herein, the add-on in question is performed for a predefined time, after which the add-on is no longer performed.
It is especially advantageous that thanks to the evaluation of the acceleration signals at right angles to the direction of driving, in the event of misusesxe2x80x94i.e., abrupt driving maneuvers and no-fire (no-deployment) crashesxe2x80x94the method according to the present invention is disabled. In the case of large and heavy vehicles such as off-road vehicles and sport utility vehicles, in particular between 40 and 64 km/h very low deceleration values arise in the direction of driving, and, if in the case of these vehicles a deformable barrier is present, an airbag can only be reliably deployed via the basic algorithm starting from the fiftieth millisecond. Only after that instant is the barrier deformed so that the vehicle meets rigid resistance, and therefore only then does the vehicle undergo rapid deceleration. Thus a distinction relative to 15 km/h no-fire crashes can only be made reliably starting from that instant. This crash behavior is related to the relatively substantial weight of the vehiclexe2x80x94over 2 tonsxe2x80x94and its rigid structure. However, it is desirable that for example a 64 km/h collision should result in deployment before 40 milliseconds have elapsed. As the deceleration in the direction of driving is insufficient for an early deployment decision without deploying for 15 km/h crashes as well, the central y acceleration signal is used as a further criterion. The y acceleration signal has modest dynamics overall, but in the case of a 40-64 km/h collision it is greater compared to the y acceleration signal for a 15 km/h collision. Two functions can be derived from this feature, which are the subject matter of the method according to the present invention: The integrator add-on function makes use of the influenceable absolute integrator of the central y signal, and under certain initial conditions performs add-ons to the integrator of the x acceleration. The absolute value of the y signal is used in the threshold pointer add-on function to perform add-ons to the threshold pointer of the x acceleration signal. Here, too, initial conditions are defined, e.g., so that the function is not activated if a misuse is involved. Furthermore, it is advantageous that the acceleration values and the corresponding integrated acceleration values at right angles to the direction of driving, i.e., the y acceleration values, are compared with a definable parameter, and if the acceleration values are greater than this parameter, the difference between the two values is calculated. The differences are then added up successively until the disable instant. Below, the summed values are referred to as the dynamics of the y acceleration signal. Add-ons to the x integrator are performed as a function of this dynamics of the y acceleration signal. The amount of the add-ons is predefined via a characteristic curve. The add-ons are performed starting from the instant at which the dynamics enters a definable time threshold window. The add-ons cease to be performed once the disable instant has been reached. Thus if the dynamics passes by the window, the function is disabled. If, by a first instant, the dynamics has reached higher values than the upper threshold, the function stays disabled, because a misuse is present, e.g., a hammer blow or a high-speed frontal crash having a large y component. Moreover, if, by a second instant, the dynamics reaches lower values than the lower dynamics threshold, the function is disabled, because a 15 km/h no-fire crash is present.
It is advantageous that the acceleration values are read in cyclically. Herein, the value that is greatest in terms of absolute value is held, and its amount is limited. This limiting is carried out within four time windows within which various limitation values are applied. The limited value is then added to the x acceleration value starting at the instant starting from which the limited value enters an applicable time threshold window. The add-ons cease to be performed once the disable instant or the interval time has been reached. If, by a third instant, the maximum value reaches a greater value than the upper threshold, the function stays disabled, because a misuse is present. Moreover, if, by a fourth instant, the maximum values reaches lower values than the lower dynamics threshold, the function is disabled, because a 15 km/h no-fire crash is present.
Furthermore, it is also advantageous that a device for carrying out the method according to the present invention is provided, the device having a controller, and acceleration sensors arranged centrally in the vehicle being present, these being used to determine the acceleration in the direction of driving and at right angles to the direction of driving. Herein, the acceleration sensors can be arranged either directly in the x and y directions or at an angle thereto, e.g., an angle of 45 degrees.